Due to limited resources, low and middle-income countries (LMICs) have been unable to implement World Health Organization (WHO) models for improving depression outcomes, in which community health workers (CHWs) deliver cognitive behavioral therapy (CBT) and other psychological treatments. We will develop and evaluate an mHealth intervention that can increase the reach and effectiveness of mental health care in LMICs. Building on our established foundation of collaborative mHealth research in Bolivia, we will develop and test AniMvil, a scalable mHealth service designed to monitor patients' depressive symptoms and deliver tailored behavioral activation messages derived from CBT principles. In Aim 1, we will collaborate with Bolivian mental health professionals, potential CHWs, and people with depression to develop AniMvil's mHealth components, including automated phone (IVR)- and text message (SMS)-based patient monitoring and psychoeducation, plus smartphone resources that will enable CHWs to deliver brief, structured CBT by telephone. Patients' depressive symptoms and CBT skill-practice will be reported weekly via IVR, and patients will receive tailored behavioral activation messages during those calls. Patients will report their mood daily via SMS and receive reinforcement and follow-up based on those reports. Patients with severe depression will be stepped up to receive a minimum of 3 CHW-delivered telephone CBT sessions. CHWs will use smartphone tools to: access information about CBT training, manage appointments and clinical records, share information with one another and their supervisor regarding challenging cases, and request supervisory consults. In Aim 2, we will conduct a randomized trial among 114 depressed patients to determine the impact of AniMvil on depression-related outcomes. Patients will be randomized to the intervention or an enhanced control condition in which they receive written materials and report daily mood information via automated SMS. The primary outcome will be the proportion of patients with remitted depression at 3 months. SMS daily mood reports in both arms will be a key secondary outcome. The trial includes an evaluation of intervention processes such as use of mHealth tools by patients and CHWs, and program costs. By emphasizing collaborative engagement with Bolivian co-investigators, we will increase their capacity for independent mHealth scientific discovery. If effective, AniMvil could improve population-based mental health care in LMICs, as well as the efficiency and quality of CHW training and supervision for delivering WHO-recommended treatments. Evidence from this study will directly inform decision-making by the Bolivian Ministry of Mental Health regarding national scale-up and financial sustainability. Results also will guide the design of larger effectiveness trials and international dissemination efforts. By combining SMS/IVR monitoring and patient activation with smartphone support for CHWs and supervisors, Animvil can serve as a prototype for mHealth services that increase access to care management for LMIC patients with other high priority non-communicable diseases.